Transistor regulator ( Rv providing a bias current)

Description

In the simplest case a common collector transistor (emitter follower) is used with the base of the regulating transistor connected directly to the voltage reference. The output voltage of the stabilizer is equal to the zener diode voltage less the base–emitter voltage of the transistor. Rv provides a bias current for both the zener diode and the transistor. The current in the diode is minimum when the load current is maximum. The circuit designer must choose a minimum voltage that can be tolerated across Rv, bearing in mind that the higher this voltage requirement is, the higher the required input voltage,and hence the lower the efficiency of the regulator. On the other hand, lower values of Rv lead to higher power dissipation in the diode and to inferior regulator characteristics.